U.S. patent application number 10/902681 was filed with the patent office on 2006-02-02 for chlorine dioxide solution generator.
This patent application is currently assigned to PureLine Treatment Systems, LLC. Invention is credited to Jerry J. Kaczur, Chenniah Nanjundiah, Timothy J. O'Leary.
Application Number | 20060021872 10/902681 |
Document ID | / |
Family ID | 35730916 |
Filed Date | 2006-02-02 |
United States Patent
Application |
20060021872 |
Kind Code |
A1 |
O'Leary; Timothy J. ; et
al. |
February 2, 2006 |
Chlorine dioxide solution generator
Abstract
A chlorine dioxide solution generator, which injects a chlorine
dioxide solution into a pressurized fluid system, including an
absorption loop for effecting the dissolution of chlorine dioxide
into a liquid stream. The chlorine dioxide gas source can include
an anolyte loop and a catholyte loop. The generator avoids or
eliminates the introduction of air or other gases that can cause
corrosion in the process distribution system.
Inventors: |
O'Leary; Timothy J.;
(Huntington Beach, CA) ; Kaczur; Jerry J.; (North
Miami Beach, FL) ; Nanjundiah; Chenniah; (San Diego,
CA) |
Correspondence
Address: |
MCANDREWS HELD & MALLOY, LTD
500 WEST MADISON STREET
SUITE 3400
CHICAGO
IL
60661
US
|
Assignee: |
PureLine Treatment Systems,
LLC
|
Family ID: |
35730916 |
Appl. No.: |
10/902681 |
Filed: |
July 29, 2004 |
Current U.S.
Class: |
204/193 ;
205/499; 205/500 |
Current CPC
Class: |
C25B 1/26 20130101 |
Class at
Publication: |
204/193 ;
205/499; 205/500 |
International
Class: |
C25B 1/26 20060101
C25B001/26 |
Claims
1. A chlorine dioxide solution generator comprising: (a) a chlorine
dioxide gas source; and (b) an absorption loop for effecting the
dissolution of chlorine dioxide into a liquid stream; wherein said
absorption loop is fluidly connected to said chlorine dioxide gas
source.
2. The chlorine dioxide solution generator of claim 1, wherein said
absorption loop comprises a gas transfer device for directing a
chlorine dioxide gas stream from said chlorine dioxide gas source
to a chlorine dioxide absorber tank.
3. The chlorine dioxide solution generator of claim 2, wherein said
absorber tank comprises an upper portion and a lower portion, said
chlorine dioxide gas and a process water entering said absorber
tank at said lower portion of said absorber tank, with at least
some of said chlorine dioxide gas absorbing into solution with said
process water to form a chlorine dioxide solution.
4. The chlorine dioxide solution generator of claim 3, wherein said
chlorine dioxide solution exits said absorber tank at said upper
portion of said absorber tank.
5. The chlorine dioxide solution generator of claim 4, wherein a
residual of said chlorine dioxide gas exits said upper portion of
said absorber tank and recirculates into a chlorine dioxide gas
generator loop.
6. The chlorine dioxide solution generator of claim 3, wherein said
chlorine dioxide solution is substantially free of reactant
feedstock constituents.
7. The chlorine dioxide solution generator of claim 3, wherein said
chlorine dioxide solution is substantially neutral in pH and
substantially free from reaction byproducts.
8. The chlorine dioxide solution generator of claim 3, wherein said
process water is substantially demineralized.
9. The chlorine dioxide solution generator of claim 3, wherein said
process water is produced by reverse osmosis.
10. The chlorine dioxide solution generator of claim 4, wherein
said chlorine dioxide solution exits said absorber tank via a
process delivery pump.
11. The chlorine dioxide solution generator of claim 3, wherein at
least one flow switch associated with said absorber tank controls
inflow of said process water.
12. The chlorine dioxide solution generator of claim 3, wherein at
least one flow switch on said absorber tank controls gas flow
through said absorber.
13. The chlorine dioxide solution generator of claim 1, wherein
said chlorine dioxide gas source comprises an anolyte loop and a
catholyte loop, said catholyte loop fluidly connected to said
anolyte loop via a common electrochemical component.
14. The chlorine dioxide solution generator of claim 13, wherein
said anolyte loop comprises: (a) a reactant feedstock stream; (b)
at least one electrochemical cell fluidly connected to said
feedstock stream, said electrochemical cell system having a
positive end and a negative end, said reactant feedstock stream
directed through said at least one electrochemical cell to produce
a chlorine dioxide solution; and (c) a stripper column, said
chlorine dioxide solution directed from said positive end of said
at least one electrochemical cell into said stripper column, said
stripper column producing at least one of a chlorine dioxide gas
stream and excess chlorine dioxide solution, said excess chlorine
dioxide solution directed out of said stripper column and
recirculated with said reactant feedstock stream into said at least
one electrochemical cell, said chlorine dioxide gas stream exiting
said stripper column directed to said absorption loop.
15. The chlorine dioxide solution generator of claim 14, wherein
said reactant feedstock is a chlorite solution having a chlorite
concentration of up to the maximum amount capable of being
dissolved in said reactant feedstock.
16. The chlorine dioxide solution generator of claim 14, wherein
sodium chlorite is present in said reactant feedstock in a
concentration between 5 percent and 25 percent by weight.
17. The chlorine dioxide solution generator of claim 13, wherein
said catholyte loop extends from said negative end of at least one
electrochemical cell, said catholyte loop comprising: (a) a
demineralized water feed source fluidly connected to the negative
end of said at least one electrochemical cell, said demineralized
water feed source having a positive ionic constituent imparted
thereto from a reaction of a reactant feedstock in said at least
one electrochemical cell to produce an ionic solution byproduct;
and (b) a byproduct tank, said ionic solution byproduct directed
from said negative end of said at least one electrochemical cell to
said byproduct tank, said ionic solution byproduct directed out of
said byproduct tank and recirculated with said demineralized water
into said at least one electrochemical cell.
18. The chlorine dioxide solution generator of claim 17, wherein
said reaction of said reactant feedstock produces a byproduct gas,
said byproduct gas directed from said negative end of said at least
one electrochemical cell.
19. The chlorine dioxide solution generator of claim 17, wherein
said byproduct gas is diluted with ambient air and exhausted from
said generator.
20. The chlorine dioxide solution generator of claim 17, wherein
said byproduct solution in said byproduct tank is diluted.
21. The chlorine dioxide solution generator of claim 1, wherein
said chlorine dioxide gas source and said absorption loop operate
to allow introduction of a substantially pure chlorine dioxide
solution into a pressurized water system.
22. The chlorine dioxide solution generator of claim 21, wherein
said pressurized water system operates at pressures ranging from 1
psi to 100 psi (6.9 kPa to 689 kPa).
23. The chlorine dioxide solution generator of claim 21, wherein
said pressurized water system operates at pressures ranging from 30
psi to 100 psi (206.8 kPa to 689 kPa).
24. The chlorine dioxide solution generator of claim 21, wherein
said pressurized water system operates at pressures ranging from 50
psi to 100 psi (344.7 kPa to 689 kPa).
25. The chlorine dioxide solution generator of claim 21, wherein
said pressurized water system operates at pressures greater than
100 psi (689 kPa).
26. The chlorine dioxide solution generator of claim 1, wherein
said absorption loop inhibits introduction of air into a
pressurized water system.
27. The chlorine dioxide solution generator of claim 1, further
comprising a programmable logic control system.
28. A chlorine dioxide solution generator comprising: (a) a
chlorine dioxide gas generator loop; (b) an absorption loop, said
absorption loop fluidly connected to said chlorine gas generator
loop, said absorption loop comprising a gas transfer pump, said gas
transfer pump directing a substantially pure chlorine dioxide gas
stream from said chlorine gas generator loop to a chlorine dioxide
absorber tank, said absorber tank having an upper portion and a
lower portion, said substantially pure chlorine dioxide gas stream
and a process water entering said absorber tank at said lower
portion of said absorber tank, at least some of said substantially
pure chlorine dioxide gas absorbing into solution with said process
water to form a chlorine dioxide solution, said chlorine dioxide
solution exiting said absorber tank at said upper portion of said
absorber tank, a residual stream of substantially pure chlorine
dioxide gas exiting said upper portion of said absorber tank and
circulating back into said chlorine dioxide gas generator loop.
29. A chlorine dioxide solution generator comprising: (a) an
anolyte loop; (b) a catholyte loop fluidly connected to said
anolyte loop via a common electrochemical component; and (c) an
absorption loop, said absorption loop fluidly connected to said
anolyte loop, said absorption loop comprising a gas transfer pump,
said gas transfer pump directing a substantially pure chlorine
dioxide gas stream from said anolyte loop to a chlorine dioxide
absorber tank, said absorber tank having an upper portion and a
lower portion, said substantially pure chlorine dioxide gas stream
and a process water stream entering said absorber tank at said
lower portion of said absorber tank, at least some of said
substantially pure chlorine dioxide gas absorbing into solution
with said process water stream to form a chlorine dioxide solution,
said chlorine dioxide solution exiting said absorber tank at said
upper portion of said absorber tank, a residual stream of
substantially pure chlorine dioxide gas exiting said upper portion
of said absorber tank and circulating into said anolyte loop.
30. A chlorine dioxide solution generator comprising: (a) an
anolyte loop, said anolyte loop comprising a reactant feedstock
fluidly connected to at least one electrochemical cell, said at
least one electrochemical cell having a positive end and a negative
end, said at least one electrochemical cell producing an output of
chlorine dioxide solution from said reactant feedstock stream, said
chlorine dioxide solution directed from said positive end of said
at least one electrochemical cell into a stripper column, said
stripper column producing at least one of a substantially pure
chlorine dioxide gas stream and an excess chlorine dioxide
solution, said excess chlorine dioxide solution circulated with
said reactant feedstock into said at least one electrochemical
cell, said substantially pure chlorine dioxide gas stream exhausted
from said stripper column via a transfer pump; (b) a catholyte
loop, said catholyte loop fluidly connected to said negative end of
said at least one electrochemical cell, said catholyte loop
comprising a demineralized water source, said demineralized water
source connected to said negative end of said at least one
electrochemical cell, said demineralized water source having a
positive ionic constituent imparted thereto from a reaction of a
reactant feedstock in said at least one electrochemical cell to
produce an ionic solution byproduct stream, said ionic solution
byproduct stream directed from said negative end of said at least
one electrochemical cell to a byproduct tank, said ionic solution
byproduct stream circulated with said demineralized water source
from said byproduct tank to said at least one electrochemical cell;
and (c) an absorption loop, said absorption loop fluidly connected
to said anolyte loop, said absorption loop comprising said gas
transfer pump for directing said substantially pure chlorine
dioxide stream from said stripper column to a chlorine dioxide
absorber tank, said absorber tank having an upper portion and a
lower portion, said substantially pure chlorine dioxide gas stream
and a process water stream entering said absorber tank at said
lower portion of said absorber tank, at least some of said
substantially pure chlorine dioxide gas absorbing into solution
with said process water stream to form a chlorine dioxide solution,
said chlorine dioxide solution exiting said absorber tank at said
upper portion of said absorber tank, a residual stream of
substantially pure chlorine dioxide gas exiting said upper portion
of said absorber tank and circulating into said stripper column of
said anolyte loop.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to chlorine dioxide
generators. More particularly, the present invention relates to a
chlorine dioxide generator that produces a chlorine dioxide
solution for use in water treatment systems.
BACKGROUND OF THE INVENTION
[0002] Chlorine dioxide (ClO.sub.2) has many industrial and
municipal uses. When produced and handled properly, ClO.sub.2 is an
effective and powerful biocide, disinfectant and oxidizer.
[0003] ClO.sub.2 is extensively used in the pulp and paper industry
as a bleaching agent, but is gaining further support in such areas
as disinfection in municipal water treatment. Other applications
can include use as a disinfectant in the food and beverage
industries, wastewater treatment, industrial water treatment,
cleaning and disinfection of medical wastes, textile bleaching,
odor control for the rendering industry, circuit board cleansing in
the electronics industry, and uses in the oil and gas industry.
[0004] In water treatment applications, ClO.sub.2 is primarily used
as a disinfectant for surface waters with odor and taste problems.
It is an effective biocide at low concentrations and over a wide pH
range. ClO.sub.2 is desirable because when it reacts with an
organism in water, chlorite results, which studies have shown poses
no significant adverse risk to human health. The use of chlorine,
on the other hand, can result in the creation of chlorinated
organic compounds when treating water. Chlorinated compounds are
suspected to increase cancer risk.
[0005] Producing ClO.sub.2 gas for use in a chlorine dioxide water
treatment process is desirable because there is greater assurance
of ClO.sub.2 purity when in the gas phase. ClO.sub.2 is, however,
unstable in the gas phase and will readily undergo decomposition
into chlorine gas (Cl.sub.2), oxygen gas (O.sub.2), and heat. The
high reactivity of ClO.sub.2 generally requires that it be produced
and used at the same location. ClO.sub.2 is, however, soluble and
stable in an aqueous solution.
[0006] ClO.sub.2 can be prepared by a number of ways, generally
through a reaction involving either chlorite (ClO.sub.2.sup.-) or
chlorate (ClO.sub.3.sup.-) solutions. The ClO.sub.2 created through
such a reaction is often refined to generate ClO.sub.2 gas for use
in the water treatment process. The ClO.sub.2 gas is then typically
educed into the water selected for treatment. Eduction occurs where
the ClO.sub.2 gas, in combination with air, is mixed with the water
selected for treatment.
[0007] For many water treatment systems, the eduction process
satisfactorily introduces ClO.sub.2 gas directly into the process
water. Problems can occur, however, with such water treatment
systems. One problem can occur when air is simultaneously
introduced into a water system while educing the ClO.sub.2 gas. A
tremendous corrosion potential results because oxygen from the air
is added into the system. Another problem can occur when
introducing ClO.sub.2 gas into a pressurized water system. Treating
water in pressurized systems can be difficult when using educed
ClO.sub.2 gas, since high-pressure booster pumps may be needed
along with high-performance eductors. This not only increases cost,
but also raises maintenance concerns, since high-performance
eduction systems can be unreliable as operating pressures near 30
to 50 pounds per square inch (psi) or above (206.8 to 344.7
kilopascal (kPa) or above).
[0008] A need exists for a reliable chlorine dioxide generator that
allows ClO.sub.2 to be introduced into pressurized water systems.
Furthermore, a need exists for a chlorine dioxide generator that
reduces or minimizes the potential for corrosion problems that can
be associated with water systems.
SUMMARY OF THE INVENTION
[0009] A chlorine dioxide solution generator comprises a chlorine
dioxide gas source; and an absorption loop for effecting the
dissolution of chlorine dioxide into a liquid stream. The
absorption loop is fluidly connected to the chlorine dioxide gas
source.
[0010] In a preferred embodiment of the chlorine dioxide solution
generator, the absorption loop comprises a gas transfer device for
directing a chlorine dioxide gas stream from the chlorine dioxide
gas source to a chlorine dioxide absorber tank. In another
embodiment, the absorber tank comprises an upper portion and a
lower portion, the chlorine dioxide gas and a process water
entering the absorber tank at the lower portion of the absorber
tank, at least some of the chlorine dioxide gas absorbing into
solution with the process water to form a chlorine dioxide
solution. In another embodiment, the chlorine dioxide solution
exits the absorber tank at the upper portion of the absorber tank.
In another embodiment, a residual of the chlorine dioxide gas exits
the upper portion of the absorber tank and recirculates into a
chlorine dioxide gas generator loop.
[0011] In a preferred embodiment, the chlorine dioxide solution
from the chlorine dioxide solution generator is substantially free
of reactant feedstock constituents. In another embodiment, the
chlorine dioxide solution is substantially neutral in pH and
substantially free from reaction byproducts. In another embodiment,
the process water for the chlorine dioxide solution generator is
substantially demineralized. Alternatively, the process water of
the chlorine dioxide solution generator is produced by reverse
osmosis.
[0012] In a preferred embodiment, the chlorine dioxide solution
exits the chlorine dioxide solution generator absorber tank via a
process delivery pump. In another embodiment, at least one flow
switch associated with the absorber tank controls inflow of the
process water to the chlorine dioxide solution generator. In
another embodiment, at least one flow switch on the absorber tank
controls gas flow through the absorber.
[0013] In a preferred embodiment, the chlorine dioxide gas source
of the chlorine dioxide solution generator comprises an anolyte
loop and a catholyte loop, with the catholyte loop fluidly
connected to the anolyte loop via a common electrochemical
component. The anolyte loop comprises a reactant feedstock stream;
at least one electrochemical cell fluidly connected to the
feedstock stream, the electrochemical cell system having a positive
end and a negative end, the reactant feedstock stream directed
through the at least one electrochemical cell to produce a chlorine
dioxide solution, and a stripper column. The chlorine dioxide
solution is directed from the positive end of the at least one
electrochemical cell into the stripper column. The stripper column
produces at least one of a chlorine dioxide gas stream and excess
chlorine dioxide solution, and the excess chlorine dioxide solution
is directed out of the stripper column and recirculated with the
reactant feedstock stream into the at least one electrochemical
cell, with the chlorine dioxide gas stream exiting the stripper
column directed to the absorption loop. In another embodiment, the
reactant feedstock is a chlorite solution having a chlorite
concentration of up to the maximum amount capable of being
dissolved in the reactant feedstock. In another embodiment, sodium
chlorite is present in the reactant feedstock in a concentration
between 5 percent and 25 percent by weight.
[0014] In a preferred embodiment, the catholyte loop of the
chlorine dioxide solution generator extends from the negative end
of at least one electrochemical cell. The catholyte loop comprises
a demineralized water feed source fluidly connected to the negative
end of the at least one electrochemical cell, with the
demineralized water feed source having a positive ionic constituent
imparted thereto from a reaction of a reactant feedstock in the at
least one electrochemical cell to produce an ionic solution
byproduct, and a byproduct tank. The ionic solution byproduct is
directed from the negative end of the at least one electrochemical
cell to the byproduct tank, with the ionic solution byproduct
directed out of the byproduct tank and recirculated with the
demineralized water into the at least one electrochemical cell. In
another embodiment, the reaction of the reactant feedstock produces
a byproduct gas, with the byproduct gas directed from the negative
end of the at least one electrochemical cell. The byproduct gas is
diluted with ambient air and exhausted from the generator. In
another embodiment, the byproduct solution of the chlorine dioxide
solution generator in the byproduct tank is diluted.
[0015] In a preferred embodiment, the chlorine dioxide gas source
and the absorption loop of the chlorine dioxide solution generator
operate to allow introduction of a substantially pure chlorine
dioxide solution into a pressurized water system. In another
embodiment, the absorption loop of the chlorine dioxide solution
generator inhibits introduction of air into a pressurized water
system.
[0016] In a preferred embodiment, the chlorine dioxide solution
generator further comprises a programmable logic control
system.
[0017] In a preferred embodiment, a chlorine dioxide solution
generator comprises a chlorine dioxide gas generator loop. The
chlorine dioxide solution generator further comprises an absorption
loop. The absorption loop is fluidly connected to the chlorine gas
generator loop, with the absorption loop comprising a gas transfer
pump. The gas transfer pump directs a substantially pure chlorine
dioxide gas stream from the chlorine gas generator loop to a
chlorine dioxide absorber tank. The absorber tank has an upper
portion and a lower portion, with the substantially pure chlorine
dioxide gas stream and a process water entering the absorber tank
at the lower portion of the absorber tank, with at least some of
the substantially pure chlorine dioxide gas absorbing into solution
with the process water to form a chlorine dioxide solution. The
chlorine dioxide solution exits the absorber tank at the upper
portion of the absorber tank, with a residual stream of
substantially pure chlorine dioxide gas exiting the upper portion
of the absorber tank and circulating back into the chlorine dioxide
gas generator loop.
[0018] In another embodiment, a chlorine dioxide solution generator
comprises an anolyte loop. The anolyte loop comprises a reactant
feedstock fluidly connected to at least one electrochemical cell,
with the at least one electrochemical cell having a positive end
and a negative end. The at least one electrochemical cell produces
an output of chlorine dioxide solution from the reactant feedstock
stream, with the chlorine dioxide solution directed from the
positive end of the at least one electrochemical cell into a
stripper column. The stripper column produces at least one of a
substantially pure chlorine dioxide gas stream and an excess
chlorine dioxide solution, with the excess chlorine dioxide
solution circulated with the reactant feedstock into the at least
one electrochemical cell. The substantially pure chlorine dioxide
gas stream exhausts from the stripper column via a transfer pump.
The chlorine dioxide solution generator further comprises a
catholyte loop. The catholyte loop is fluidly connected to the
negative end of the at least one electrochemical cell. The
catholyte loop comprises a demineralized water source, with the
demineralized water source connected to the negative end of the at
least one electrochemical cell. The demineralized water source has
a positive ionic constituent imparted thereto from a reaction of a
reactant feedstock in the at least one electrochemical cell to
produce an ionic solution byproduct stream. The ionic solution
byproduct stream directed from the negative end of the at least one
electrochemical cell to a byproduct tank, with the ionic solution
byproduct stream circulated with the demineralized water source
from the byproduct tank to the at least one electrochemical cell.
The chlorine dioxide solution generator further comprises an
absorption loop. The absorption loop is fluidly connected to the
anolyte loop. The absorption loop comprises the gas transfer pump
for directing the substantially pure chlorine dioxide stream from
the stripper column to a chlorine dioxide absorber tank. The
absorber tank has an upper portion and a lower portion, with the
substantially pure chlorine dioxide gas stream and a process water
stream entering the absorber tank at the lower portion of the
absorber tank, with at least some of the substantially pure
chlorine dioxide gas absorbing into solution with the process water
stream to form a chlorine dioxide solution. The chlorine dioxide
solution exits the absorber tank at the upper portion of the
absorber tank, with a residual stream of substantially pure
chlorine dioxide gas exiting the upper portion of the absorber tank
and circulating into the stripper column of the anolyte loop.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a process flow diagram of an embodiment of the
present chlorine dioxide solution generator.
[0020] FIG. 2 is a process flow diagram of an anolyte loop of an
embodiment of the present chlorine dioxide solution generator.
[0021] FIG. 3 is a process flow diagram of a catholyte loop of an
embodiment of the present chlorine dioxide solution generator.
[0022] FIG. 4 is a process flow diagram of an absorption loop of an
embodiment of the present chlorine dioxide solution generator.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT(S)
[0023] FIG. 1 illustrates a process flow diagram of an embodiment
of the present chlorine dioxide solution generator 100. The process
flow of FIG. 1 consists of three sub-processes including an anolyte
loop 102, a catholyte loop 104, and an absorption loop 106. The
purpose of the anolyte loop 102 is to produce a chlorine dioxide
(ClO.sub.2) gas by oxidation of chlorite, and the process can be
referred to as a ClO.sub.2 gas generator loop. The ClO.sub.2 gas
generator loop is essentially a ClO.sub.2 gas source. Various
sources of ClO.sub.2 are available and known in the water treatment
field. The catholyte loop 104 of the ClO.sub.2 gas generator loop
produces sodium hydroxide and hydrogen gas by reduction of water.
Once the ClO.sub.2 gas is produced in the ClO.sub.2 gas generator
loop, the ClO.sub.2 gas is transferred to the absorption loop 106
where the gas is further prepared for water treatment objectives.
The process can be operated through a program logic control (PLC)
system 108 that can include displays.
[0024] In this application, the term "absorb" refers to the process
of dissolving or infusing a gaseous constituent into a liquid,
optionally using pressure to effect the dissolution or infusion.
Here, ClO.sub.2 gas, which is produced in the ClO.sub.2 gas
generator loop, is "absorbed" (that is, dissolved or infused) into
an aqueous liquid stream directed through absorption loop 106.
[0025] FIG. 2 illustrates an anolyte loop 102 in an embodiment of
the chlorine dioxide solution generator 100. The contribution of
the anolyte loop 102 to the ClO.sub.2 solution generator is to
produce a ClO.sub.2 gas that is directed to the absorption loop 106
for further processing. The anolyte loop 102 embodiment presented
in FIG. 2 is for a chlorine dioxide gas produced using a reactant
feedstock 202. In a preferred embodiment, a 25 percent by weight
sodium chlorite (NaClO.sub.2) solution can be used as the reactant
feedstock 202. However, feedstock concentrations ranging from 0
percent to a maximum solubility (40 percent at 17 degrees Celsius
in the embodiment involving NaCl.sub.2), or other suitable method
of injecting suitable electrolytes, can be employed.
[0026] The reactant feedstock 202 is connected to a chemical
metering pump 204 which delivers the reactant feedstock 202 to a
recirculating connection 206 in the anolyte loop 102. The
recirculating connection 206 in the anolyte loop connects a
stripper column 208 to an electrochemical cell 210. The delivery of
the reactant feedstock 202 can be controlled using the PLC system
108. The PLC system 108 can be used to activate the chemical
metering pump 204 according to signals received from a pH sensor
212. The pH sensor is generally located along the recirculating
connection 206. A pH setpoint can be established in the PLC system
108 and once this setpoint is reached, the delivery of reactant
feedstock 202 may either start or stop.
[0027] The reactant feedstock 202 is delivered to a positive end
214 of the electrochemical cell 210 where the reactant feedstock is
oxidized to form a ClO.sub.2 gas, which is dissolved in an
electrolyte solution along with other side products. The ClO.sub.2
solution with the side products is directed out of the
electrochemical cell 210 to the top of the stripper column 208
where a pure ClO.sub.2 is stripped off in a gaseous form from the
other side products. Side products or byproducts may include
chlorine, chlorates, chlorites and/or oxygen. The pure ClO.sub.2
gas is then removed from the stripper column under a vacuum using a
gas transfer pump 216, or analogous gas transfer device (such as,
for example, a vacuum-based device), where it is delivered to the
adsorption loop 106. The remaining solution is collected at the
base of the stripper column 208 and recirculated back across the pH
sensor 212 where additional reactant feedstock 202 may be added.
The process with the reactant feedstock and/or recirculation
solution being delivered into the positive end 214 of the
electrochemical cell 210 is then repeated.
[0028] Modifications to the anolyte loop process can be made that
achieve similar results. As an example, an anolyte hold tank can be
used in place of a stripper column. In such a case, an inert gas or
air can be blown over the surface or through the solution to
separate the ClO.sub.2 gas from the anolyte. As another example,
chlorate can be reduced to produce ClO.sub.2 in a cathode loop
instead of chlorite. The ClO.sub.2 gas would then similarly be
transferred to the absorption loop. In a further example, ClO.sub.2
can be generated by purely chemical generators and transferred to
an absorption loop for further processing.
[0029] FIG. 3 illustrates a catholyte loop 104 in an embodiment of
a chlorine dioxide solution generator 100. The catholyte loop 104
contributes to the ClO.sub.2 solution generator 100 by handling
byproducts produced from the electrochemical reaction of the
reactant feedstock 202 solution in the anolyte loop 102. As an
example, where a sodium chlorite (NaClO.sub.2) solution is used as
the reactant feedstock 202, sodium ions from the anolyte loop 102
migrate to the catholyte loop 104 through a cationic membrane 302,
in the electrochemical cell 210, to maintain charge neutrality.
Water in the catholyte is reduced to produce hydroxide and hydrogen
(H.sub.2) gas. The resulting byproducts in the catholyte loop 104,
in the example of a NaClO.sub.2 reactant feedstock, are sodium
hydroxide (NaOH) and hydrogen gas. The byproducts are directed to a
byproduct tank 304.
[0030] In an embodiment of the catholyte loop 104 in the example of
a NaClO.sub.2 reactant feedstock, a soft (that is, demineralized)
water source 306 can be used to dilute the byproduct NaOH using a
solenoid valve 308 connected between the soft water source 306 and
the byproduct tank 304. The solenoid valve 308 can be controlled
with the PLC system 108. In a preferred embodiment, the PLC system
108 can use a timing routine that maintains the NaOH concentration
in a range of 5 percent to 20 percent. When the byproduct tank 304
reaches a predetermined level above the base of the tank 304, the
diluted NaOH byproduct above that level is removed from the
catholyte loop 104.
[0031] In the example of a NaClO.sub.2 reactant feedstock, the
catholyte loop 104 self circulates using the lifting properties of
the H.sub.2 byproduct gas formed during the electrochemical process
and a forced water feed from the soft water source 306. The H.sub.2
gas rises up in the byproduct tank 304 where there is a hydrogen
disengager 310. The H.sub.2 gas can be diluted with air in the
hydrogen disengager 310 to a concentration of less than 0.5
percent. The diluted H.sub.2 gas can be discharged from the
catholyte loop 104 and the chlorine dioxide solution generator 100
using a blower 312.
[0032] In another embodiment, dilute sodium hydroxide can be fed
instead of water to produce concentrated sodium hydroxide. Oxygen
or air can also be used as a reductant instead of water to reduce
overall operation voltage since oxygen reduces at lower voltage
than water.
[0033] The reaction of the anolyte loop 102 and catholyte loop 104
in the embodiment illustrated in FIGS. 2 and 3 is represented by
the following net chemical equation:
2NaClO.sub.2(aq)+2H.sub.2O.fwdarw.2ClO.sub.2(gas)+2NaOH.sub.(aq)+H.sub.2(-
gas) The NaClO.sub.2 is provided by the reactant feedstock 202 of
the anolyte loop 102. The NaOH and H.sub.2 gas are byproducts of
the reaction in the catholyte loop 104. The ClO.sub.2 solution
along with the starting unreacted NaClO.sub.2 and other side
products are directed to the stripper column for separating into
ClO.sub.2 gas as part of the anolyte loop 102 process. Chlorite
salts other than NaClO.sub.2 can be used in the anolyte loop.
[0034] FIG. 4 illustrates an absorption loop 106 of an embodiment
of the chlorine dioxide solution generator 100. The absorption loop
106 processes the ClO.sub.2 gas from the anolyte loop into a
chlorine dioxide solution that is ready to be directed to the water
selected for treatment.
[0035] The ClO.sub.2 gas is removed from the stripper column 208 of
the anolyte loop 102 using the gas transfer pump 216. In a
preferred embodiment, a gas transfer pump 216 can be used that is
"V" rated at 75 Torr (10 kPa) with a discharge rate of 34 liters
per minute. The vacuum and delivery rate of the gas transfer pump
216 may vary depending upon the free space in the stripper column
208 and desired delivery rate of chlorine dioxide solution.
[0036] The ClO.sub.2 gas removed from the stripper column 208 using
the gas transfer pump 216 is directed to an absorber tank 402 of
absorption loop 106. In a preferred embodiment, the discharge side
404 of the gas transfer pump 216 delivers ClO.sub.2 gas into a 0.5
inch (13-mm) PVC injection line 406 external to the absorber tank
402. The injection line 406 is an external bypass for fluid between
the lower to the upper portions of the absorption tank 402. A gas
injection line can be connected to the injection line 406 using a
T-connection 408. Before ClO.sub.2 gas is directed to the absorber
tank 402, the tank 402 is filled with water to approximately 0.5
inch (13 mm) below a main level control 410. The main level control
410 can be located below where the injection line 406 connects to
the upper portion of the absorption tank 402. Introducing ClO.sub.2
gas into the injection line 406 can cause a liquid lift that pushes
newly absorbed ClO.sub.2 solution up past a forward-only flow
switch 412 and into the absorber tank 402. The flow switch 412
controls the amount of liquid delivered to the absorber tank 402.
The absorber tank 402 has a main control level 410 to maintain a
proper tank level. In addition to the main control level, safety
control levels can be used to maintain a high level 414 and low
level 416 of liquid where the main control level fails. A process
delivery pump 418 feeds the ClO.sub.2 solution from the absorption
tank 402 to the end process without including air or other gases.
The process delivery pump 418 is sized to deliver a desired amount
of water per minute. The amount of ClO.sub.2 gas delivered to the
absorber tank 402 is set by the vacuum and delivery rate set by the
gas transfer pump 216.
[0037] The PLC system 108 can provide a visual interface for the
operator to operate the entire chlorine dioxide solution generator
100. The PLC system 108 can automatically control the continuous
operation and safety of the production of ClO.sub.2 solution. The
PLC system can set flow rates for the anolyte and catholyte loops
102, 104. The safety levels of the absorber tank 402 can also be
enforced by the PLC system 108. A PLC system 108 can also control
the power for achieving a desired current in an embodiment using an
electrochemical cell 210. In a preferred embodiment, the current
ranges from 0 to 100 amperes, although currents higher than this
average are possible. The amount of current determines the amount
of ClO.sub.2 gas that is produced in the anolyte loop 102. The
current of the power supply can be determined by the amount of
chlorine dioxide that is to be produced. A PLC system 108 can also
be used to monitor the voltage of the electrochemical cell 210. In
a preferred embodiment, the electrochemical cell 210 may be shut
down when the voltage exceeds a safe voltage level. In another
preferred embodiment, 5 volts can be considered a safe voltage
level.
[0038] Another operation that can be monitored with the PLC system
108 is the temperature of the electrochemical cell 210. If
overheating occurs, the PLC system 108 shuts down the
electrochemical cell 210.
[0039] The PLC system 210 can also monitor the pH of the anolyte
using a pH sensor 212. During operation of the electrochemical cell
210, the pH of the solution circulating in the anolyte loop 102
decreases as hydrogen ions are generated. In the exemplary
embodiment of the NaClO.sub.2 reactant feedstock, when the pH goes
below 5, additional reactant feedstock is added using the PLC
system. Control of pH can also be handled by adding a reactant that
depletes the pH where pH may be too high.
[0040] In another embodiment, the transfer line from the gas
transfer pump 216 can be connected to the absorber tank 402
directly without the injection line 406, and may allow for
increasing the transfer rate of the pump. Other embodiments can
include a different method of monitoring the liquid level in the
absorber tank 402. For example, an ORP (oxidation and reduction
potential) can be dipped in the absorber tank 402. ORP can be used
to monitor the concentration of chlorine dioxide in the solution in
the absorber tank 402. The PLC system 108 can be used to set a
concentration level for the chlorine dioxide as monitored by ORP,
which provides an equivalent method of controlling the liquid level
in the absorber tank 402. Optical techniques such as photometers
can also be used to control the liquid level in the absorber tank
402. The absorption loop can be a part of the chlorine dioxide
generator or it can be installed as a separate unit outside of the
chlorine dioxide generator. In another embodiment, process water
can be fed directly in the absorber tank 402 and treated water can
be removed from the absorber tank 402. The process water can
include a demineralized, or soft, water source 420 and the process
water feed can be controlled using a solenoid valve 422.
[0041] The process flow illustrated in FIGS. 1, 2 and 3 are based
on ClO.sub.2 gas produced using electrochemical cells and a sodium
chlorite solution. ClO.sub.2 gas can be made using many different
processes that would be familiar to a person skilled in water
treatment technologies. Such processes include, but are not limited
to, acidification of chlorite, oxidation of chlorite by chlorine,
oxidation of chlorite by persulfate, use of acetic anhydride on
chlorite, use of sodium hypochlorite and sodium chlorite, use of
dry chlorine/chlorite, reduction of chlorates by acidification in
the presence of oxalic acid, reduction of chlorates by sulfur
dioxide, and the ERCO R-2.RTM., R-3.RTM., R-5.RTM., R-8.RTM.,
R-10.RTM. and R-11.RTM. processes.
[0042] While particular elements, embodiments and applications of
the present invention have been shown and described, it will be
understood, of course, that the invention is not limited thereto
since modifications can be made by those skilled in the art without
departing from the scope of the present disclosure, particularly in
light of the foregoing teachings.
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